Wire discharge-machining apparatus with parallel cutting wires

ABSTRACT

A wire machining method includes: a wire electrode set as cutting wires provided in parallel with a distance between the cutting wires of which a predetermined regional part faces a workpiece; a machining power source that generates a pulse-shaped machining voltage; and plural feeder units that are electrically connected to the plural cutting wires respectively of the wire electrode and supply the machining voltage between the cutting wires and the workpiece respectively. The feeder units are arranged such that a direction of a current passed to at least a part of the cutting wires becomes a direction different from a direction of a current passed to other cutting wires.

TECHNICAL FIELD

The present invention relates to a wire discharge-machining apparatus,and more particularly relates to a wire discharge-machining method forcutting a workpiece into plural sheet members at a time by winding awire electrode in parallel between plural guide rollers and bygenerating electric discharges between wire electrodes arranged inparallel and the workpiece, and the wire discharge-machining methodachieves machining in high shape precision while preventing the wireelectrodes from being warped by magnetic fields generated due tocurrents flowing to the parallel wire electrodes. The present inventionalso relates to a manufacturing method of a member of which highmachining precision is required, such as a semiconductor wafer and asolar cell wafer.

BACKGROUND ART

When slice machining a wafer from a pillar-shaped workpiece by a wiredischarge-machining apparatus, there has been proposed an approach toimprove productivity of slice machining the workpiece by simultaneouslygenerating electric discharges between the workpiece and cutting wiresby individually passing a current to each cutting wire among manycutting wires arranged by winding a wire electrode in parallel betweenplural guide rollers (see, for example, Patent documents 1 and 3).

In a semiconductor wafer manufacturing apparatus having the aboveconfiguration, magnetic fields are generated around parallel wireelectrodes when a machining current flows to the wire electrodes, anelectromagnetic force works on adjacent wire electrodes, and then warpsthe wire electrodes in some cases. On the other hand, in a conventionalsemiconductor wafer manufacturing apparatus such as that described inPatent document 1, currents are supplied from both sides of theworkpiece to parallel wires. Therefore, no countermeasure is takenagainst warping of wire electrodes due to the electromagnetic force ofthe wire electrodes.

Meanwhile, regarding the electromagnetic force working on the wireelectrodes, for example, Patent document 2 describes, in a configurationof a wire discharge-machining apparatus, a method of using anelectromagnetic force in an operation to return a wire electrode to adirection of avoiding a short-circuit when the wire electrode isshort-circuited with a workpiece. That is, magnetic fields are generatedaround a workpiece by passing an auxiliary current to the workpiece, andthe wire electrode is restored by using the magnetic fields and anelectromagnetic force of a machining current flowing to the wireelectrode. By controlling the strength and flow direction of anauxiliary current according to a machining state, the strength ofmagnetic fields is changed to control an electromagnetic force workingon the wire electrode.

However, in the wire discharge-machining apparatus having aconfiguration such as that described in Patent document 2, the apparatusdoes not assume magnetic fields working between wire electrodes bypassing a machining current to parallel wire electrodes arranged bywinding a wire electrode around plural guide rollers like in the presentinvention. Therefore, in the control of an auxiliary current to theworkpiece, an electromagnetic force working on the wire electrode cannotbe reduced by the magnetic fields described above. Further, controllingsizes and flow directions of auxiliary currents supplied to theworkpiece during machining results in changing energy of electricdischarge machining, and this becomes a cause of degrading machiningprecision and reducing its machining speed.

The technique proposed in Patent document 2 is to improve an avoidingoperation of a short-circuit state, but does not become a method ofpreventing warping of wire electrodes due to an electromagnetic forcewhen machining using a wire electrode.

PRIOR ART DOCUMENTS Patent Documents

-   Patent document 1: Japanese Patent Application Laid-open No.    2000-94221-   Patent document 2: Japanese Patent Application Laid-open No.    S61-95827-   Patent document 3: Japanese Patent Application Laid-open No.    H9-248719

DISCLOSURE OF INVENTION Problem to be Solved by the Invention

Let us assume a case that currents flow concurrently in the samedirection to parallel wire electrodes in a wire discharge-machiningapparatus having a wire electrode arranged in parallel by winding thewire electrode around plural guide rollers as described above. Forexample, it is assumed that a current I flows to 500 parallel wireelectrodes arranged at an interval r. In this case, wire electrodes atboth ends receive the largest force, and a force F received by thesewire electrodes is derived by the following equation.

$\begin{matrix}{F = {\sum\limits_{n = 1}^{499}\;\frac{\mu_{0}I^{2}}{2\pi\;{nr}}}} & (1)\end{matrix}$When an average current of 2 amperes flows to parallel wire electrodesat a 400-micrometer pitch, the force F becomes as follows.μ₀=4π×10⁻⁷ kg·m/C²I=2 A=2 C/sr=400×10⁻⁶ mthenF=0.01361 N/m  (2)

That is, a uniform load of 0.0136 Newton is applied to the wireelectrodes per length of 1 meter, and this uniform load warps the wireelectrodes. While this warping is normally corrected by giving apredetermined tension to the wire electrodes, when the tension appliedis too large, wire electrodes are disconnected. The limit of tensionthat can be applied is different according to the material and diameterof the wire electrode. Therefore, even when the uniform load is thesame, a warping amount changes depending on the used wire electrode.

For example, in a case of a brass wire with a diameter of 0.2millimeter, a tension that can be applied is about 15 Newtons, andwarping of wire electrodes per length of 1 meter due to the uniform loadbecomes about 113 micrometers. In a case of a piano wire with a diameterof 0.1 millimeter, a tension that can be applied is about 5 Newtons, andwarping of wire electrodes per length of 1 meter due to the uniform loadbecomes about 340 micrometers. However, because this is a case that anaverage current flowing to wire electrodes is 2 amperes and because acurrent is supplied in a pulse shape in actual electric dischargemachining, a current larger than 2 amperes flows to the wire electrodes.Further, in the equation (1), the force F received by the wireelectrodes becomes larger than a calculation value described above,because the force F works by a square of the current I. That is, awarping amount of wire electrodes becomes larger than the abovecalculation value, and an occurrence of warping at a pitch higher thanthat of parallel wire electrodes is anticipated. An electromagneticforce varies and a warping amount of wire electrodes also variesdepending on a pulse-shaped current. Because a workpiece is machinedwhile oscillating the parallel wire electrodes, a machining trench widthbecomes large and the workpiece cannot be cut out thin.

Warping of wire electrodes does not occur at only a machining startstage, and a machining current flowing to the wire electrodes byelectric discharge machining generates a magnetic field, and this causesan electromagnetic force to work on other parallel wire electrodes. In astate that parallel wire electrodes enter the workpiece along progressof machining, even when the workpiece is present between parallel wireelectrodes, a magnetic field generated from other parallel wireelectrodes is not shielded and an electromagnetic force works on theother parallel wire electrodes to warp the wire electrodes, if theworkpiece is not a magnetic substance.

The present invention has been achieved to solve the above problems, andan object of the present invention is to obtain a wiredischarge-machining apparatus and a wire discharge-machining method forachieving high-precision machining by preventing an occurrence ofwarping due to an electromagnetic force working on parallel wireelectrodes. Another object of the present invention is to obtain amethod of processing a material in a wafer shape while preventingwarping of wires when manufacturing semiconductor wafers and solar cellwafers.

Means for Solving Problem

In order to solve the aforementioned problems, a wiredischarge-machining apparatus and a wire discharge-machining method,semiconductor wafer manufacturing apparatus and semiconductor wafermanufacturing, and solar-cell wafer manufacturing method according toone aspect of the present invention is construed in such a manner as toinclude: a wire electrode set as cutting wires provided in parallel witha distance therebetween and facing a workpiece; a machining power sourcethat generates a pulse-shaped machining voltage; and a plurality offeeder units that are electrically connected to the cutting wiresrespectively of the cutting wire electrode and supply the machiningvoltage between the cutting wires and the workpiece respectively,wherein in the parallel cutting wires, the feeder units are arrangedsuch that a direction of a current passed to at least a part of thecutting wires becomes a direction different from a direction of acurrent passed to other cutting wires.

In the wire discharge-machining apparatus and the method thereof, thesemiconductor wafer manufacturing apparatus and the method thereof, andthe solar-cell wafer manufacturing apparatus and the method thereof,directions of currents flowing to adjacent cutting wires are setmutually opposite to offset strengths of magnetic fields generated bythe wire electrodes in parallel wire electrodes. By using this offset ofmagnetic fields, machining currents are supplied such that currentsflowing to parallel wire electrodes do not have the same direction inall wire electrodes.

Effect of the Invention

According to the present invention, in the parallel wire electrodes ofwhich predetermined regional parts provided in parallel with a distancefrom each other face a workpiece and become cutting wires, the feederunits are arranged such that directions of currents supplied to adjacentcutting wires become mutually opposite. Therefore, magnetic fieldsgenerated by machining currents flowing to the cutting wires by electricdischarge machining are either offset by magnetic fields generated bycurrents flowing to adjacent cutting wires in opposite directions orweakened. As a result, an electromagnetic force working on the cuttingwires is reduced, and thus warping of wire electrodes is suppressed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a configuration of a wiredischarge-machining apparatus according to a first embodiment of thepresent invention.

FIG. 2 is an explanatory diagram of a configuration of power feeding toparallel wire electrodes according to the first embodiment of thepresent invention.

FIG. 3 is an explanatory diagram of a configuration of power feeding toparallel wire electrodes according to a second embodiment of the presentinvention.

FIG. 4 is a perspective view of a wire discharge-machining apparatusaccording to a third embodiment of the present invention.

FIG. 5 is an explanatory diagram of a configuration of power feeding toparallel wire electrodes according to a third embodiment of the presentinvention.

BEST MODE(S) FOR CARRYING OUT THE INVENTION First Embodiment

Configurations and operations according to embodiments of the presentinvention are explained below. FIG. 1 is a perspective view of a wiredischarge-machining apparatus according to a first embodiment of thepresent invention. In the wire discharge-machining apparatus accordingto the first embodiment, a wire electrode 2 reeled out from a wirebobbin 1 is sequentially wound between plural guide rollers 3 a to 3 dat plural times with a small distance between wounded parts of the wireelectrode 2, thereby forming plural cutting wires. A distance betweencutting wires formed by winding the wire electrode 2 becomes a machiningwidth (a wafer thickness) of a workpiece 8. That is, the workpiece 8 iscut in an electrically discharged manner by each cutting wire by cuttingfeeding the workpiece 8 to each cutting wire while supplying a voltagebetween each cutting wire and the workpiece 8 in a state that theworkpiece 8 is set opposite to each cutting wire with a predetermineddistance between the cutting wires. Accordingly, the workpiece 8 is cutinto plural wafers. The workpiece 8 is a material to be sliced into thinsheets, and includes metals such as tungsten and molybdenum that becomea sputtering target, ceramics such as polycrystalline silicon carbideused for various structural members, semiconductor materials such asmonocrystalline silicon and polycrystalline silicon carbide that becomea semiconductor device wafer, and solar cell materials such asmonocrystalline silicon and polycrystalline silicon that become a solarcell wafer. The semiconductor materials and the solar cell materialsgenerally have a specific resistance equal to or higher than 0.0001 Ωcm,and materials that can be machined in an electrically discharged mannergenerally have a specific resistance equal to or lower than 100 Ωcm,preferably equal to or lower than 10 Ωcm. Therefore, in the presentinvention, materials having a specific resistance equal to or higherthan 0.0001 Ωcm and equal to or lower than 10 Ωcm are preferable as thesemiconductor materials and the solar cell materials. In an exampleshown in FIG. 1, although one wire electrode 2 is wound around pluralguide rollers, plural cutting wires can be formed by folding back onewire electrode 2 instead of this method, and a specific configurationthereof is not particularly limited.

In the first embodiment, the plural guide rollers 3 a to 3 d arearranged in parallel with a distance between them in an axial linedirection. The guide roller 3 a and the guide roller 3 b are provided athighest positions, and the guide roller 3 c is provided at a lowestposition below the guide roller 3 b. The guide roller 3 d is providedbelow the guide roller 3 a arranged with the guide roller 3 c.

The wire electrode 2 is ejected from a wire ejection roller 5 afterbeing wound at a predetermined number of times. A portion of the wireelectrode 2 between the guide roller 3 a and the guide roller 3 bbecomes a cutting wire 2 a capable facing the workpiece 8 and machiningthe workpiece 8. As shown in FIG. 1, the workpiece 8 is arrangedopposite to the cutting wire 2 a at a small distance between the cuttingwire 2 a and the workpiece 8 to perform an electric discharge-machiningprocess. A portion of the wire electrode 2 between the guide roller 3 band the guide roller 3 c becomes a power feeding wire 2 b to which avoltage (a machining voltage) to perform electric discharge machining issupplied.

A voltage (a machining voltage) to perform electric discharge machiningis supplied to the power feeding wire 2 b of the wire electrode 2 from amachining power source 6 via feeders 7A and 7B, and a voltage issupplied between the power feeding wire 2 b and the workpiece 8. Themachining power source 6 is configured by plural machining power-sourceunits 61 capable of independently supplying a voltage. The feeders 7Aand 7B are configured by plural feeder units 71 and 72, respectivelyinsulated from each other, and can independently supply a voltage toeach cutting wire 2 a. The plural machining power-source units 61capable of independently supplying a voltage to parallel wire electrodesare connected to a control device (not shown) of the wiredischarge-machining apparatus.

Naturally, a voltage application polarity can be suitably invertedaccording to need, in a similar manner to that of conventional wiredischarge machining. A position of the workpiece 8 is controlled by aposition control device (not shown) to have a small distance from thewire electrode 2 wound between the guide rollers 3 a to 3 d. Therefore,an appropriate electric-discharge gap length is maintained for theworkpiece 8. A machining liquid (not shown) is supplied between theworkpiece 8 and the wire electrode 2 by blowing or by immersion in asimilar manner to that of normal wire discharge machining.

Power feeding to parallel wire electrodes in the wiredischarge-machining apparatus according to the first embodiment of thepresent invention is explained next. FIG. 2 depicts only a periphery ofa part that feeds power to the parallel wire electrodes to make clear astate of power feeding to the parallel wire electrodes and the workpieceaccording to the first embodiment. When supplying machining currents tothe workpiece 8 from the plural machining power-source units 61, powerfeeding lines of all of the machining power-source units 61 areconnected to the workpiece 8. Other power feeding lines of the machiningpower-source units 61 are connected to feeder units (the feeder unit 71or the feeder unit 72) corresponding to the cutting wires 2 a,respectively, and are connected to feeder units in a configurationdescribed below. Two feeder units 71 and 72 provided in each of thecutting wire 2 a are arranged at positions to sandwich the workpiece 8as shown in FIG. 2. The cutting wires 2 a are supported to bridgebetween the two feeder units 71 and 72. Other power feeding lines of themachining power-source units 61 are alternately connected to the twofeeder units 71 and 72 as shown in FIG. 2. When a power feeding line isconnected to the feeder unit 71 corresponding to a certain cutting wire2 a, a power feeding line is connected to the feeder unit 72, not thefeeder unit 71, in the cutting wire 2 a adjacent to this cutting wire.With this configuration, when directions of currents flowing to parallelcutting wires 2 a become mutually opposite directions between adjacentcutting wires 2 a, feeder units to which power feeding lines are notconnected function as wire guides (supporting members), and arrangeplural cutting wires 2 a in parallel in cooperation with feeder units towhich power feeding lines are connected.

According to this configuration, in a state that electric dischargemachining occurs between the plural cutting wire 2 a and the workpiece8, and machining currents concurrently flow to the cutting wires 2 a,flowing directions of machining currents become mutually oppositedirections. Therefore, magnetic fields generated by the cutting wires 2a are offset by magnetic fields generated by mutually adjacent cuttingwires 2 a. Consequently, an electromagnetic force that becomes a forceto warp the cutting wires 2 a by working on the cutting wires 2 a can besuppressed.

As described above, according to the configuration of the firstembodiment, one wire electrode 2 is wound between the plural guiderollers 3 a to 3 d to form the plural cutting wires 2 a. The machiningpower source 6 and the feeders 7A and 7B are provided to individuallyfeed power to each cutting wire 2 a and such that directions of currentsflowing to the cutting wires 2 a become mutually opposite betweenadjacent cutting wires 2 a. Accordingly, warping of wire electrodes atboth ends of the parallel cutting wires 2 a can be reduced, and the wireelectrodes at both ends of the parallel cutting wires 2 a are not warpedduring machining. As a result, a machined part of the workpiece 8 doesnot become in an arc shape but becomes a straight line. Consequently,machining precision improves, and thicknesses of wafers cut out at atime from the workpiece 8 by the parallel cutting wires 2 a becomeuniform.

Second Embodiment

In the first embodiment described above, a system of preventing warpingof the cutting wires 2 a due to an electromagnetic force is explained.According to this system, one wire electrode 2 is wound between theplural guide rollers 3 a to 3 d to form the plural cutting wires 2 a.The machining power source 6 and the feeders 7A and 7B are provided toindividually feed power to each cutting wire 2 a and to set directionsof currents flowing to the cutting wires 2 a mutually opposite betweenadjacent cutting wires 2 a. That is, the system according to the firstembodiment supplies power to the parallel cutting wires 2 a such thatflow directions of currents become mutually opposite between adjacentcutting wires 2 a, thereby offsetting magnetic fields generated by thecutting wires 2 a. This system can prevent warping of the cutting wires2 a due to an electromagnetic force, and can improve machining shapeprecision. In a second embodiment, a modification of the firstembodiment to suppress warping of the cutting wires 2 a due to anelectromagnetic force in a power feeding system to parallel cuttingwires 2 a is explained.

FIG. 3 depicts a part that feeds power to the parallel wire electrodesaccording to the second embodiment. A basic device configuration of thesecond embodiment is the same as that of the first embodiment shown inFIG. 2, and a connection system of power feeding lines from themachining power-source units 61 to feeders arranged opposite to theworkpiece 8 are different, as shown in FIG. 3. Therefore, in thefollowing explanations, configurations different from those of the firstembodiment shown in FIGS. 1 and 2 are mainly explained and explanationsof identical configurations will be omitted.

As shown in FIG. 3, in the second embodiment, power feeding lines at apolarity side not connected to the workpiece 8 out of two polarities ofthe machining power-source units 61 are connected to the feeder units 71and 72. In this case, in the first embodiment, the feeder units 71 and72 aligned at the same side of the workpiece 8 are alternately connectedto the cutting wires 2 a to alternately feed power to the feeder units71 and 72 opposite to the cutting wires 2 a. In the second embodiment,the feeder units 71 and 72 at a power-feeding-line connection side arenot alternately connected to the cutting wires 2 a. Two adjacent cuttingwires 2 a are set as one group, and power feeding lines at the samepolarity side are connected to the feeder units 71 and 72 arranged atthe same side, in this one group, that is, these two cutting wires 2 a.The cutting wire 2 a adjacent to this one group of the cutting wires 2 aand the cutting wire 2 a further adjacent to this cutting wire 2 a areset as one group. Power feeding lines of the machining power-sourceunits 61 are connected to the feeder units 71 and 72 arranged at theopposite side of the above group of the cutting wires 2 a, in the groupof two cutting wires 2 a.

Instead of setting adjacent two parallel wires as one group as describedabove, plural (three, or four, five onwards) cutting wires 2 a can beset as one group. In this way, the feeder units 71 and 72 areelectrically connected to the wire electrodes 2 of the cutting wires 2 asuch that adjacent plural cutting wires 2 a are set as each group,directions of currents passed to the cutting wires 2 a of the same groupare set to be the same directions, and directions of currents passed tothe cutting wires 2 a of adjacent groups become mutually oppositedirections. In this case, feeder units to which power feeding lines arenot connected function as wire guides (supporting members), and arrangeplural cutting wires 2 a in parallel on the same plane in cooperationwith feeder units to which power feeding lines are connected.

According to this configuration, in a state that electric dischargemachining occurs between the parallel cutting wires 2 a and theworkpiece 8 and that machining currents flow to the parallel cuttingwires 2 a, magnetic fields generated by the machining currents areweakened by magnetic fields generated in peripheral cutting wires 2 a.Therefore, an electromagnetic force working on the cutting wires 2 a towarp the cutting wires 2 a can be reduced.

As described above, according to the second embodiment, effects similarto those of the first embodiment are obtained, and power feeding linescan be easily arranged in a power feeding configuration to the parallelcutting wires 2 a because power is fed such that plural cutting wires 2a of parallel cutting wires 2 a are handled as one group and currentflow directions become opposite between groups.

Third Embodiment

In the first embodiment described above, a system of preventing warpingof the cutting wires 2 a due to an electromagnetic force is explained.According to this system, one wire electrode 2 is wound between theplural guide rollers 3 a to 3 d to form the plural cutting wires 2 a.The machining power source 6 and the feeders 7A and 7B are provided toindividually feed power to each cutting wire 2 a and to set directionsof currents flowing to the cutting wires 2 a mutually opposite betweenadjacent cutting wires 2 a. That is, the system according to the firstembodiment supplies power to the parallel cutting wires 2 a such thatflow directions of currents become mutually opposite between adjacentcutting wires 2 a, thereby offsetting magnetic fields generated by thecutting wires 2 a. This system can prevent warping of the cutting wires2 a due to an electromagnetic force, and can improve machining shapeprecision.

In the second embodiment, in the power feeding system to the parallelcutting wires 2 a, plural parallel cutting wires 2 a are handled asgroups, power is fed to the cutting wires 2 a constituting these groupssuch that currents flow in the same direction, and current directionspassed to the cutting wires 2 a of adjacent groups become mutuallyopposite. In this system, warping of the cutting wires 2 a due to anelectromagnetic force can be suppressed and machining shape precisioncan be improved, by weakening the strength of magnetic fields generatedby currents flowing to the cutting wires 2 a.

In a third embodiment, there is explained a power feeding system to thecutting wires 2 a which does not pass currents alternately or inopposite directions for each of the few cutting wires but reduces as faras possible the number of cutting wires 2 a to which currents inopposite directions are passed, thereby reducing the magnetic fieldstrength and suppressing warping of the cutting wires 2 a due to anelectromagnetic force.

FIG. 4 is a perspective view of a wire discharge-machining apparatusaccording to the third embodiment of the present invention. As shown inFIG. 4, a basic configuration of the third embodiment is identical tothat of the first embodiment shown in FIG. 1. Therefore, in thefollowing explanations, configurations different from those of the firstembodiment shown in FIG. 1 are mainly explained and explanations ofidentical configurations will be omitted.

Also in the third embodiment, in a similar manner to those of the firstand second embodiments, the wire electrode 2 reeled out from the wirebobbin 1 is wound between the plural guide rollers 3 a to 3 d at pluraltimes with a small distance between the wire electrodes, thereby formingplural wire running systems. Finally, the wire electrode 2 is wound at apredetermined number of times, and is ejected from the wire ejectionroller 5. In this case, in the third embodiment, a portion of the wireelectrode 2 between the guide roller 3 a and the guide roller 3 bbecomes the cutting wire 2 a to machine the workpiece 8. As shown inFIG. 4, the workpiece 8 is arranged opposite to the cutting wires 2 awith a small distance between the cutting wires 2 a and the workpiece 8to perform an electric discharge-machining process. A portion of thewire electrodes 2 between the guide roller 3 b and the guide roller 3 cbecomes the power feeding wires 2 b to which a voltage (a machiningvoltage) to perform electric discharge machining is supplied. A voltage(a machining voltage) to perform electric discharge machining issupplied to the power feeding wires 2 b of the wire electrode 2 from themachining power source 6 via the feeders 7A and 7B, and a voltage issupplied between the power feeding wires 2 b and the workpiece 8. Themachining power source 6 is configured by plural machining power-sourceunits 61 capable of independently supplying a voltage. The feeders 7Aand 7B are configured by the plural feeder units 71 and 72, respectivelyinsulated from each other, and can independently supply a voltage toeach cutting wire 2 a. The plural machining power-source units 61capable of independently supplying a voltage to parallel cutting wires 2a are connected to a control device (not shown) of the wiredischarge-machining apparatus.

Power feeding to the parallel wire electrodes in the wiredischarge-machining apparatus according to the third embodiment of thepresent invention is explained next. FIG. 5 depicts a state that, in thefirst embodiment, in feeding power of the machining power source 6configured by the machining power-source units 61 to the workpiece 8,power feeding lines connected to the same polarity side of all themachining power-source units 61 are connected to the workpiece 8. Powerfeeding lines from another same polarity side of the machiningpower-source units 61 are connected to feeder units shown in FIG. 5.Power feeding lines from a polarity side of the machining power-sourceunits 61 not connected to the workpiece 8 are connected to feeder unitsarranged at the same side as the workpiece 8, except wire electrodes atboth ends among the parallel cutting wires 2 a. On the other hand, tofeed power to the cutting wires 2 a at both ends among the parallelcutting wires 2 a, power feeding lines from the polarity side of themachining power-source units 61 not connected to the workpiece 8 areconnected to feeder units arranged to support at two points the cuttingwires 2 a machining the workpiece 8, at positions sandwiching theworkpiece 8 as shown in FIG. 5. In this case, feeder units to whichpower feeding lines are not connected function as wire guides(supporting members), and arrange plural cutting wires 2 a in parallelon the same plane in cooperation with feeder units to which powerfeeding lines are connected.

An operation of the third embodiment is explained next. FIG. 5 depictsperipheral parts of a feeder unit configured by the parallel cuttingwires 2 a and the workpiece 8, the guide rollers 3 a and 3 b, thefeeders 7A and 7B, and the machining power-source units 61. In theconfiguration shown in FIG. 5, when an electric discharge occurs betweenthe cutting wires 2 a and the workpiece 8, currents from the machiningpower-source units 61 pass through the power feeding lines and flow tothe cutting wires 2 a via the feeder units 71 and 72. At this time,currents in the same direction flow to other parallel cutting wires 2 aexcluding cutting wires A1 and A2 at both ends, among the cutting wires2 a arranged in parallel. Magnetic fields are generated at the peripheryof the cutting wires 2 a by the currents, and an electromagnetic forceworks on the cutting wires 2 a in which currents flow. Particularly, inthe parallel cutting wires 2 a to which currents flow in the samedirection, the largest electromagnetic force works on cutting wires B1and B2 positioned at both ends, thereby warping the cutting wires 2 a.However, according to the power feeding system of the third embodiment,power is fed to the cutting wires A1 and A2 at both ends of the parallelwires to pass currents in a direction opposite to that of currents inother parallel cutting wires 2 a, such as B1 and B2. Therefore, magneticfields generated by currents flowing to the cutting wires A1 and A2effectively weaken the magnetic field strength working on the cuttingwires B1 and B2 at both ends of the parallel cutting wires 2 a to whichthe currents flow in the same direction. Accordingly, an electromagneticforce working on the cutting wires B1 and B2 is suppressed, and warpingof the cutting wires 2 a is prevented. At the same time, the magneticfield strength working on the cutting wires A1 and A2 is weakened, andan electromagnetic force working on the cutting wires A1 and A2 issuppressed, thereby preventing warping of the cutting wires 2 a.

As explained above, according to the third embodiment, a direction of acurrent flowing to each one cutting wire 2 a positioned at both ends ofparallel cutting wires 2 a is set opposite to a direction of currentsflowing to remaining parallel cutting wires 2 a excluding these twocutting wires 2 a. Therefore, an electromagnetic force working on thecutting wires 2 a can be reduced, and warping of the cutting wires 2 acan be prevented.

In the first to third embodiments, as an example, there have beenexplained a wire discharge-machining apparatus having plural wirerunning systems provided by winding the wire electrode 2 between pluralguide rollers with a distance between the wire running systems. However,the present invention is not limited thereto, and the first to thirdembodiments can be also applied to a wire discharge-machining apparatusincluding three or more wire electrodes that generate an electricdischarge between a workpiece and the wire electrodes, even when thewire electrodes are not wound up.

An arrangement positional relationship among the guide rollers, thefeeder units, and the workpiece or a stage (not shown) on which theworkpiece is mounted in the first to third embodiments is explained. Forexample, the guide rollers can be arranged between the feeder unitsarranged at both sides of a workpiece or a stage on which the workpieceis mounted and the workpiece or the stage on which the workpiece ismounted, as shown in FIGS. 1 and 4.

Alternatively, as shown in FIGS. 2, 3, and 5, the feeder units can bearranged at both sides of the workpiece or of the stage on which theworkpiece is mounted, and the guide rollers can be arranged at sides ofthe feeder units thereof where the workpiece or the stage on which theworkpiece is mounted is not arranged.

When semiconductor materials such as monocrystalline silicon andpolycrystalline silicon carbide, solar cell materials such asmonocrystalline silicon and polycrystalline silicon, ceramics such aspolycrystalline silicon carbide, and sputtering target materials such astungsten and molybdenum are machined by the above wiredischarge-machining method, an electromagnetic force working betweenwires during electric discharge machining is offset or reduced, and thuswarping of wire electrodes is prevented. Therefore, plural wafers can becut out at a time in high size precision.

EXPLANATIONS OF LETTERS OR NUMERALS

-   -   1 Wire bobbin    -   2 Wire electrode    -   2 a Cutting wire    -   2 b Power feeding wire    -   3 a, 3 b, 3 c, 3 d Guide roller    -   5 Wire ejection roller    -   6 Machining power source    -   7A, 7B Feeder    -   8 Workpiece    -   61 Machining power-source unit    -   71, 72 Feeder unit

The invention claimed is:
 1. A wire discharge-machining apparatuscomprising: a wire electrode set as cutting wires provided in parallelwith a distance therebetween and facing a workpiece; a machining powersource that generates a machining voltage; and a plurality of feederunits that are electrically connected to the cutting wires respectivelyof the wire electrode and supply the machining voltage between thecutting wires and the workpiece respectively, wherein the plurality offeeder units are arranged at both sides of the workpiece, the both sidesincluding a first side and a second side, at least one feeder unit onthe first side and at least one feeder unit on the second side areconnected to respective power feeder lines from the machining powersource, in the cutting wires, the feeder units are arranged such that adirection of a current passed to at least a part of the cutting wiresbecomes a direction different from a direction of a current passed toother cutting wires, and the feeder units are provided on the first sideand the second side for each of the cutting wires, and the machiningvoltage from the machining power source is connected to only one of thefeeder units on either side of each of the cutting wires to therebysupply the machining voltage between the cutting wires and theworkpiece.
 2. The wire discharge-machining apparatus according to claim1, wherein the feeder units are electrically connected to the wireelectrode by having feeders connected to the cutting wires alternatelyarranged on the first side and the second side such that directions ofcurrents passing through the cutting wires become opposite between thecutting wires adjacent to each other.
 3. The wire discharge-machiningapparatus according to claim 1, wherein the feeder units areelectrically connected to the wire electrode by having the feedersconnected to the cutting wires alternately arranged on the first sideand the second side such that a plurality of adjacent cutting wires areset as groups, directions of currents passed to cutting wires in a samegroup become a same direction, and directions of currents passed tocutting wires in adjacent groups become opposite to each other.
 4. Thewire discharge-machining apparatus according to claim 1, wherein thefeeder units are electrically connected to the wire electrode by havingthe feeders connected to the cutting wires alternately arranged on thefirst side and the second side such that a current direction in theoutermost two of the cutting wires is opposite to a current direction ofall the other cutting wires.
 5. The wire discharge-machining apparatusaccording to claim 1, wherein the feeder units on the first and thesecond sides including the feeder units not connected to the powerfeeder line function as supporting members of the wire electrode.
 6. Thewire discharge-machining apparatus according to claim 5, wherein thefeeder units not connected to the power feeder lines cause the cuttingwires to cooperate with the feeder units connected to the power feederlines.
 7. The wire discharge-machining apparatus according to claim 1,wherein the feeder units provided at both sides of the cutting wires areconnected in such a manner that these feeder units are arranged in aline in a direction orthogonal to the cutting wires.
 8. The wiredischarge-machining apparatus according to claim 1, wherein at least oneof plural guide rollers that winds cutting wires is arranged between oneof the plurality of feeder units and the workpiece.
 9. The wiredischarge-machining apparatus according to claim 1, wherein guiderollers that wind the cutting wires are arranged at sides of the feederunits that are farther away from the workpiece than the feeder units.